1) The tests I am referring to are the AES tests referred to by desktop (presumably reports are available from the AES for the standard fees..)
2) Actually devising a test that meets these requirements is extremely difficult - takes a LOT of effort..
Speakers need to be set up in an anechoic chamber, the chamber needs to be tested to ensure that all reflections are absorbed at all frequencies
The speakers/setup need to be tested for linearity at all frequencies up to the test limit, and need to also meet other audiophile test criteria (transient response, phase response, etc....)
Obviously the microphones used for this testing need to somehow be tested themselves...
3) Showing that any tone can affect any other tone is simply a matter of physics... I suggest http://en.wikipedia.org/wiki/Intermodulation
as an initial reading point. (particularly the section on passive IM and IM in audio applications)
4) Intermodulation does not require that we be able to hear the fundamental tone - it only requires that we be able to sense (given the thrust of the discussion, hearing might be a somewhat limited term) a change.... And if the products of the intermodulation are distortions residing within the 20-20kHz range then there is a high likelihood that we can indeed hear them.
5) Of particular interest is the subsequent question (with reference to Rap's posting...) - which is how does the brain then interpret the additional signals?
Is the additional sense of space and air frequently provided by cartridges with extended phase linear response, due to the high frequencies reproduced (albeit at low levels) - or due to intermodulations of these signals resulting in sounds within the audio range that our brain automatically interprets as higher frequencies... ie are we wired to recognise higher frequencies by their lower frequency IM products?
And this being a very much wired in brain response, may be something that is learnt at very very early age (before 3years) - after which you either have it or not. The sight and hearing processing centres get "programmed" very early on - if they were not programmed at these early stages - it cannot be remedied later...
Which in turn would beg the question.... What early life influences would help a baby to develop "Golden Ears"?
(And yes, I tend strongly towards nurture rather than nature in that specific argument...)
Avole, I agree in questioning the audibility of material over 20kHz.... but if credible sources respond by saying that some proportion (even if it is a small %) of the population can in fact sense something happening beyond 20kHz, then my question is why and how.
The crux of the matter from your perspective, appears to be the credibility of the sources - in which case might I suggest that you look into finding the original AES material desktop mentioned.
Desktop's CV does entitle him to at least a modicum of credibility in this environment - and if you wish to question his substantially supported opinions, I would think the onus would be on you to research the material, and then come back with relevant counter arguments.
(Mate, you ain't got the troops for this battle.... go find yourself some decent cavalry then you might have a chance of outflanking him... oops .... sorry, wrong forum... I always enjoyed military strategy....)
bye for now